Apparatus for simultaneous dry desulfurization/denitrification

ABSTRACT

It is an high efficiency and low cost apparatus for simultaneous dry desulfurization and denitration ( 10 ), capable of simultaneous oxidation of nitrogen monoxide and sulfur dioxide by chain reaction with OH radical, provided with an OH radical supplying unit ( 12 ), a reactor ( 14 ), a sulfuric acid recovering unit ( 16 ), and a nitric acid recovering unit ( 18 ). Exhaust gas at 600-800° C. containing sulfur compounds from a boiler ( 2 ) is introduced into the reactor ( 14 ), nitric acid is spray-supplied from an OH radical supplying unit ( 12 ) into the reactor ( 14 ), sulfur dioxide and nitrogen monoxide are simultaneously oxidized with OH radicals generated from pyrolysis of nitric acid as an initiator to form sulfur trioxide and nitrogen dioxide, thereby exhaust gas is treated.

TECHNICAL FIELD

The present invention relates to the apparatus for simultaneous drydesulfurization and denitration to induce chain reaction using OHradicals, thereby to simultaneously oxidize nitrogen monoxide and sulfurdioxide, which is utilized for removal of such atmospheric contaminantsas nitrogen and sulfur compounds contained in exhaust gas.

BACKGROUND ART

Fossil fuels such as coal contains sulfur compounds as impurities, andmost of sulfur content is exhausted as sulfur dioxide upon combustionunder excess of oxygen. Sulfur dioxide contained in exhaust gas isgenerally removed by wet process using a scrubber to contact exhaust gaswith the mist of absorbent and absorb and remove sulfur dioxide (Refer,for example, to the Japanese laid open Patent Application (JPH10-202049-A)).

A dry exhaust gas treating method is also known which oxidizes sulfurdioxide gas by passing sulfur dioxide in exhaust gas through pulsedcorona discharge region, and removes it by adsorbing on fine powder ofcalcium oxide or others as an adsorbent (Refer, for example, to theJapanese laid open Patent Application (JP H05-228330-A)). Further, theart to convert sulfur dioxide gas to sulfur trioxide gas with vanadiumpentoxide (V₂O₅) as an oxidizing catalyst was disclosed in the Japaneselaid open Patent Application (JP 2001-11041-A).

However, by the exhaust gas treating method of wet process, big plantinvestment is required, and an apparatus itself is large-sized due torequired large amount of water, and therefore, it is not easily utilizedwhere water resource is scant. Also by the exhaust gas treating methodof dry process, high cost is required due to the use of additives andoxidative catalysts.

DISCLOSURE OF THE INVENTION

The object of the present invention is to solve such problems, and tooffer an apparatus for simultaneous dry desulfurization and denitrationof high efficiency and low cost, capable of treating exhaust gas by dryprocess without catalysts or others, and of simultaneous oxidation ofnitrogen monoxide and sulfur dioxide by chain reaction using OHradicals.

In order to achieve the above-mentioned object, an apparatus forsimultaneous dry desulfurization and denitration of the presentinvention is characterized in that, in a dry exhaust gas treatingapparatus to treat exhaust gas of high temperature, it is comprised of areactor and an OH radical supplier, and treats exhaust gas by supplyingeither OH radicals or OH radical initiators to the reactor into whichexhaust gas is introduced, and by oxidizing either sulfur or nitrogencompounds in exhaust gas, or both of them simultaneously.

In addition to the above-mentioned makeup, the reactor may be providedwith an inner and an outer tubes coaxially spaced, and a radicalsupplying inlet to supply either OH radicals or OH radical initiators toan inner tube. In the inner tube, there may be radical supplying inletsprovided in plurality at the pre-designed interval, capable ofmulti-step blow-in. The reactor is preferably provided with injectors tosupply OH radicals and OH radical initiators. It is advantageous if saidinjectors are provided in plurality with different lengths capable ofmulti-step blow-in. The reactor may also be provided with either ashower pipe or a spray nozzle, or both, to supply either OH radicals orOH radical initiators. Said reactor may be either horizontal or verticaltype. The OH radical supplier may preferably have a radical generationsource and a gas supplying system. The OH radical initiator ispreferably nitric acid. OH radicals are generated by pyrolysis of nitricacid.

According to said aspect, the sulfur compound in exhaust gas is sulfurdioxide, the nitrogen compound is nitrogen monoxide, and sulfur dioxideand nitrogen monoxide can be simultaneously oxidized with either OHradicals or OH radicals generated from OH radical initiators as theinitiator. In this case, the oxides generated from simultaneousoxidation are sulfur trioxide and nitrogen dioxide.

The apparatus for simultaneous dry desulfurization and denitration ofsuch aspect induces chain reaction with supplied OH radicals as theinitiator, simultaneously oxidizes sulfur dioxide and nitrogen monoxideto sulfur trioxide and nitrogen dioxide, and exhausts them. Therefore,the apparatus for simultaneous dry desulfurization and denitration ofthe present invention is capable of exhaust gas treating in dry processwithout using catalysts and others at high efficiency and low cost.

Further, the apparatus for simultaneous dry desulfurization anddenitration of the above-mentioned aspect is preferably provided with asulfuric acid recovery apparatus to recover sulfur trioxide formed byoxidation process of exhaust gas as either sulfuric acid or gypsum, orboth. Also, the above-mentioned apparatus for simultaneous drydesulfurization and denitration is preferably provided with a nitricacid recovery apparatus to recover nitrogen dioxide formed by oxidationprocess of exhaust gas as nitric acid. It may also be provided with anitric acid recovery apparatus to recover OH radical suppliers as nitricacid. The recovered nitric acid may be reused by recycling as OH radicalsuppliers.

Since the apparatus for simultaneous dry desulfurization and denitrationof such aspect recovers sulfuric acid from sulfur trioxide formed byoxidative treating of exhaust gas, sulfuric acid or gypsum can berecovered efficiently. Nitrogen dioxide formed by oxidative treating ofexhaust gas can also be recovered as nitric acid, and further, in casethat nitric acid is supplied as an OH radical supplier, nitric acid canbe recovered and recycled, thereby reused as an OH radical supplier.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will better be understood from the followingdetailed description and the drawings attached hereto showing certainillustrative forms of embodiment of the present invention. In thisconnection, it should be noted that such forms of embodiment illustratedin the accompanying drawings hereof are intended in no way to specify orto limit the present invention but to facilitate an explanation and anunderstanding thereof. In the drawings,

FIG. 1 is a graph showing the calculation result of temperaturedependency of SO₃ generation concentration on the added amount of NOwith HNO₃ kept constant;

FIG. 2 is a table showing the rate constants of added elementaryreactions;

FIG. 3 is a graph showing the calculated values of mole fraction ofsulfur compounds between 400 and 1000K;

FIG. 4 is a graph showing the calculation result of SO₃ generationdependency on NO addition concentration at T=750K;

FIG. 5 is a graph showing the calculation result of SO₃ generation ratedependency on HNO₃ addition concentration at T=750K;

FIG. 6 is a graph showing the calculation result of the change with timeof various chemical species in oxidation reaction of SO₂ and NO of FIG.4;

FIG. 7 is a graph showing the calculation result of sensitivitycoefficients of major elementary reactions to SO₃ concentration underthe calculation conditions of FIG. 6;

FIG. 8 is a graph showing the calculation result of the temperaturedependency of SO₃ generation concentration on the amount of added HNO₃;

FIG. 9 is a drawing showing the system makeup of an apparatus forsimultaneous dry desulfurization and denitration in accordance with thepresent invention;

FIG. 10 is a partial outline of a cross sectional view of a reactor andan OH radical supplier in accordance with a suitable embodiment;

FIG. 11 is a partial outline of a cross sectional view of a reactor andan OH radical supplier in accordance with another suitable embodiment;

FIG. 12 is an external view showing an example of an injector;

FIG. 13 is a cross sectional view showing an outline of a reactorprovided with a shower pipe;

FIG. 14 is a cross sectional view showing an outline of a verticalreactor provided with a spray nozzle;

FIG. 15 is a cross sectional view showing an outline of a horizontalreactor provided with a shower pipe; and

FIG. 16 is a cross sectional view showing an outline of a scrubber.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the suitable embodiments in accordance with the presentinvention will be described in detail with reference to FIGS. 1-16,using the same symbol for practically identical or corresponding parts.

First, the dry process of simultaneous desulfurization and denitrationis explained as the principle of an apparatus for simultaneous drydesulfurization and denitration of the present invention. As the resultof the present inventors' research on the desulfurization anddenitration method capable of easily oxidizing SO₂ and NO withoutcatalyst, efficient chemical reactions were discovered for the firsttime by various studies and calculations to oxidize sulfur dioxide (SO₂)and nitrogen monoxide (NO) contained in exhaust gas from variouscombustion ovens by gas phase chain reaction to sulfur trioxide (SO₃)and nitrogen dioxide (NO₂), using OH or OH radicals (Mitsuo Koshi, etal, “Chemical Kinetics of Homogeneous Oxidation of SO₂ in Flue Gases”,CREST International Symposium on ADVANCED DESOx PROCESS, Japan Scienceand Technology Corporation, Dec. 6, 2002, pp. 169-180).

The oxidation of SO₂ and NO in exhaust gas from various combustionovens, that is, the desulfurization and denitration method used for thepresent invention is so made up that chain reactions proceed as thechemical equations shown below.OH+SO₂+M=HOSO₂+M   (R1),HOSO₂+O₂═HO₂+SO₃   (R2),HO₂+NO═OH+NO₂   (R3), andHNO₃+M=OH+NO₂+M   (R4).

SO₂ and NO in exhaust gas are at left-hand sides of the chemicalreaction equations (R1) and (R3). Here, O₂ is oxygen gas contained inexhaust gas. M is the gas not involved in reactions, for example, N₂,and CO₂ and H₂ or the like added together with N₂.

The above-mentioned chemical reaction are explained here. As shown inchemical reaction equation (R4), OH is formed from HNO₃. OH is the hightemperature radical state in exhaust gas. If OH is supplied to chemicalreaction in equation (R1), OH, SO₂, and M react to form HOSO₂+M.

HOSO₂ formed here reacts with O₂ in exhaust gas to form HO₂ and SO₃(Refer to chemical reaction equation (R2)). In this case, since O₂concentration in exhaust gas is much higher than any other radicalspecies, the reaction rate of (R2) is higher than the reactions of otherHOSO₂ with radical species, like OH+HOSO₂, O+HOSO₂, or H+HOSO₂.

Next, HO₂ formed by chemical reaction equation (R2) reacts with NO toform HO and NO₂ (Refer to chemical reaction equation (R3)). Thus, withadded OH, chain reactions are established.

From these, the sum up of chemical reaction equations (R1)-(R3) becomesto be,SO₂+NO+O₂═SO₃+NO₂.   (R5)It is thus seen that SO₂, NO, and O₂ in exhaust gas react and they areoxidized to SO₃ and NO₂.

Thereby, SO₂ and NO in exhaust gas containing O₂ can be oxidized, asshown in chemical reaction equation (R4), to SO₃ and NO₂ by chainreaction with OH or OH radicals formed from HNO₃ pyrolysis.Consequently, since the vapor pressure and pyrolysis rate of HNO₃ arehigher than those of H₂O₂, and its handling is also easier than H₂O₂,SO₂ and NO in exhaust gas containing O₂ can be oxidized with low cost.

The simulation result of SO₂ and NO oxidation by the above-mentionedchemical reaction equations is explained next. Said simulation wasconducted by calculating the above-mentioned chemical reaction equations(R1)-(R4) by reaction mechanism of SO_(x) proposed by Mueller et al, andby adding some more elementary reactions involving HNO₃ and NO₃ (Referto M. A. Mueller, R. A. Yetter, and F. L. Dryer, Int. J. Chem. Kinet.,32, 317 (2000)).

First, the dependency of added NO quantity upon HNO₃ addition to SO₂ inexhaust gas is explained. FIG. 1 is a graph showing the calculationresult of temperature dependency of SO₃ generation concentration on theadded amount of NO with HNO₃ kept constant. In the figure, the abscissais temperature (K), and the ordinate is SO₃ concentration (ppm).

The calculation condition here is the hypothesis that the reactionproceeds in adiabatic state, and that the reaction time is one second.In this case, SO₂ concentration in exhaust gas is 2000 ppm, and HNO₃concentration is 1000 ppm. M consists of N₂, CO₂, and H₂O, and the totalpressure including O₂ in exhaust gas is 1 atm, since those of SO₂ andHNO₃ are negligible because their concentrations are trivial, and theirratio (%) isN₂: CO₂: H₂O: O₂=71:16:8:5.

FIG. 2 is a table showing the rate constants of added elementaryreactions. Added elementary reactions are, for example, the chemicalreaction equations shown below inhibiting chemical reaction equation(R4).OH+HNO₃═H₂O+NO₃   (R6), andOH+NO₃═NO₂+HO₂   (R7).

In FIG. 1, it is seen that the reaction from SO₂ to SO₃ proceeds at NO=0ppm, but its rate remarkably increases by NO addition. In case that NOconcentration is 50 ppm, the conversion from SO₂ to SO₃ (hereinaftercalled as SO₃ conversion) is maximum around T=750 K, that is, about 4%.In case of NO concentration 200 ppm, SO₃ conversion is maximum betweenT=750-770K, that is, about 6.3%. Further in case that NO concentrationis increased to 400 ppm, SO₃ conversion is lowered than at 200 ppm, andit gradually increases from 1.5% to 4.3% at T=700-820K. It is seen fromthese observations that SO₃ conversion is improved by NO additiontogether with SO₂ into exhaust gas, and that optimum NO concentrationexists for it.

In FIG. 1, the reason for maximum conversion to SO₃ at around 750Kexcept for 400 ppm of HNO₃ concentration is explained.

FIG. 3 is a graph showing the calculated values of mole fraction ofsulfur compounds between 400 and 1000K. Its ordinate is mole fraction ofsulfur compounds, and abscissa is temperature (K). It is seen from thisthat SO₃ is more stable than H₂SO₄ and SO₂ at 600-850K, and especially,its mole fraction reaches the maximum value at 650-800K. Therefore, itis conceivable that SO₂ is easily oxidized at 650-800K.

FIG. 4 is a graph showing the calculation result of SO₃ generationdependency on NO addition concentration at T=750K. In the figure, itsordinate is SO₃ concentration, and abscissa is NO concentration (ppm).The condition is same as in FIG. 1 except that HNO₃ concentration is 100ppm. It is seen that SO₃ conversion increases till NO concentration ofabout 200 ppm, and decreases with NO concentration above that.

SO₃ conversion dependency on HNO₃ concentration with addition of NO 200ppm into exhaust gas is shown next. FIG. 5 is a graph showing thecalculation result of SO₃ generation rate dependency on HNO₃ additionconcentration at T=750K. In the figure, its ordinate is SO₃concentration, and abscissa is HNO₃ concentration (ppm). The conditionis same as in FIG. 1 except that SO₂ concentration is 1000 ppm, and NOconcentration is 200 ppm. It is seen that SO₃ conversion is about 15,16, and 17%, respectively, with HNO₃ concentration 200, 300, and 400ppm. SO₃ generation increases with the increase of HNO₃ concentrationtill HNO₃ concentration of about 100 ppm. In case that HNO₃concentration is higher than about 200 ppm, SO₃ conversion tends tosaturate with respect to HNO₃ concentration. Said conversion is seen toincrease remarkably in comparison with the case of no NO addition shownin FIG. 1. In this case, NO conversion to NO₂ (hereinafter, to be calledNO₂ conversion) is 80 to 90%.

FIG. 6 is a graph showing the calculation result of the change with timeof various chemical species in oxidation reaction of SO₂ and NO of FIG.5. In the figure, its ordinate is mole fraction, and abscissa is time(second). The condition is same as in FIG. 1 except that temperature is750K, NO concentration is 200 ppm, and SO₂ concentration is 1000 ppm. Itis seen from the figure that SO₂ and NO are oxidized by HNO₃ pyrolysisto form about 0.2 second. It is also seen from this that main oxidationproducts are SO₃ and NO₂, and NO is scarcely formed, and added NO isalmost completely oxidized to NO₂.

FIG. 7 is a graph showing the calculation result of sensitivitycoefficients of major elementary reactions to SO₃ concentration underthe calculation conditions of FIG. 6. The initial conditions are same asin FIG. 6. In the figure, its ordinate is the sensitivity coefficientsof major elementary reactions to generate SO₃, and abscissa is time(second). The sensitivity coefficient S_(ij) of an elementary reaction ifor a chemical species j is given as S_(ij)=θC_(j)/θk_(i), where C_(j)is the concentration of a chemical species j, and k_(i) is a rateconstant of an elementary reaction i. It is seen from FIG. 7 that themost important reactions for SO₃ generation are chemical reactionequations (R1), (R3), and (R4) (Refer to (R1), (R3), and (R4) in FIG.7).

On the other hand, chemical reaction equations (R8) and (R9) writtenbelow are competitive chain reactions taking place with chemicalreaction equation (R1) of OH generated from HNO₃ pyrolysis, and are thechemical reactions to hinder SO₃ generation (Refer to (R8) and (R9) inFIG. 7).NO+OH+M=HONO+M   (R8)HONO+OH═H₂O+NO₂   (R9).

Also, the chemical reaction equation (R10) written below is a chaintermination reaction inducing radicals not generated, with OH generatedfrom HNO₃ pyrolysis reacting to form H₂O and O₂, and this reaction, too,acts in the direction of terminating SO₃ generation (Refer to (R10) inFIG. 7).HO₂+OH=H₂O+O₂   (R10).

Next is explained for comparison HNO₃ addition effect under thecondition only with SO₂ without NO addition into exhaust gas. FIG. 8 isa graph showing the calculation result of the temperature dependency ofSO₃ generation concentration on the amount of added HNO₃. In the figure,its abscissa is temperature (K), and ordinate is SO₃ concentration(ppm). Here, the condition is same as in FIG. 1 except that SO₂concentration in exhaust gas is 2000 ppm, and HNO₃ concentration ischanged to 100, 500, and 1000 ppm. SO₃ conversion increases with HNO₃concentration increase, and reaches 2%, which is maximum, at aboutT=750K in case of 100 ppm HNO₃ addition. Next, SO₃ conversion reaches6.5%, which is maximum, at about T=760K in case of 500 ppm as HNO₃concentration. Further, in case of 1000 ppm as HNO₃ concentration, SO₃conversion is seen to reach 8% as maximum at about T=750K.

Thus, SO₂ oxidation reaction has low efficiency with HNO₃ only withoutNO addition into exhaust gas. This is assumed as because most of OHgenerated from HNO₃ pyrolysis reacts with HNO₃ and NO₃, thereby thechain reaction does not function (Refer to chemical reaction equations(R6) and (R7)).

As explained heretofore, the desulfurization and denitration method ofSO₂ and NO in exhaust gas used in the present invention can oxidize SO₂and NO in exhaust gas containing oxygen simultaneously to SO₂ and NO₂,by inducing chain reaction with the addition of OH radicals atrelatively low temperature of 600-800K. In this case, in order toinitiate chain reaction, it is necessary to generate chemical species OHor HO₂ as chain carriers. HNO₃ is preferable as a radical initiator forsaid radical generation.

In a typical case that exhaust gas temperature is 750° C, SO₃ conversionincreases when HNO₃ conversion is increased. NO₂ conversion shows thetendency to decrease when HNO₃ concentration is over 100 ppm, but if SO₂in exhaust gas is about 1000 ppm, almost 20% of SO₂ can be converted toSO₃ by addition of 1000 ppm of HNO₃. In this case, NO₂ conversion can be80 to 90%, about four times as high as SO₃ conversion.

Next, the apparatus for simultaneous dry desulfurization and denitrationof the present invention using the desulfurization and denitrationmethod described above is explained.

FIG. 9 is a drawing showing the system structure of a dry processapparatus for simultaneous desulfurization and denitration in accordancewith the present invention. Referring to FIG. 9, an apparatus forsimultaneous dry desulfurization and denitration 10 in accordance withan embodiment of the present invention is comprised of an OH radicalsupplier 12, a reactor 14, a sulfuric acid recovery system 16, and anitric acid recovery system 18, and the exhaust gas from a boiler 2 orothers is introduced into the reactor 14. The apparatus for simultaneousdry desulfurization and denitration 10 in accordance with the presentinvention may be provided to a flue gas duct as a path of exhaust gasfrom various combustion apparatuses.

FIG. 10 is an outline of a reactor and an OH radical supplier inaccordance with a suitable embodiment. Referring to FIG. 10, a reactor20 is comprised of an inner tube 22 to introduce exhaust gas 23 at600-800° C. from the boiler 2, and an outer tube 28 which is providedwith said inner tube coaxially inside, and forming a closed spacetogether with manifolds 24 and 26 at both ends. Said inner tube isprovided at preferable positions with radical supplying inlets 21 and 27in the direction of exhaust gas introduction, that is, at symmetricalpositions with respect to coaxial direction. As shown in FIG. 10,exhaust gas 23 is supplied from one end of the inner tube 22, SO₂ and NOcontained in said exhaust gas 23 are simultaneously oxidized, and areexhausted from the other end.

The space between the inner tube 22 and the outer tube 28 is anintroducing line of OH radicals or OH radical initiators. The inner tube22 is provided with radical supplying inlets 21 and 27 at four steps,but it may be at one step depending on the scale of exhaust gastreating, or may be appropriately at many steps. Here, the arrow 25 inFIG. 10 shows the flow of OH radicals or OH initiators.

Here, multi-step reaction may be designed to proceed by furtherseparating the inner tube 22 with partition walls for each radicalsupplying inlet 21 and 27, and blowing in OH radicals or OH radicalinitiators at multi-steps in the direction from exhaust gas 23introducing side to exhaust side. Since thereby SO₂ and NO are treatedat each step, the conversions of SO₃ and NO₂ can be made almost 100%.

As is shown in FIG. 10, the OH radical supplier 12 is provided with agas supplier 32 for N₂, O₂, and NO, and with an OH radical initiatingsource 31. And the gas supplier 32 is provided with by mass flow metersand valves not shown in the figure and is controlled by the computer tosupply gases according to the pre-set flow rates and reaction processes.

Here, in order to oxidize SO₂ in exhaust gas efficiently to SO₃, it isimportant to properly adjust NO concentration. Therefore, it ispreferable to have NO controllable to 0 to about 200 ppm in said gassupplying system.

The OH radical supplier 12 is provided with a tank 34 filled with an OHradical initiator 33, HNO₃ here, a carrier gas supply line 36 to carrysaid HNO₃ 33 as vapor, and an OH radical initiator supply line 38. HNO₃may be either 100% or aqueous solution of pre-designed ratio.

Here, exhaust gas is 600-800° C., and in such temperature region, HNO₃as a radical initiator is pyrolyzed to generate OH radicals, but for thecase that the temperature of exhaust gas is low or the like, an electricfurnace 37 may be provided before inlet into the manifold 24, therebyradical initiators are surely pyrolyzed to supply OH radicals. The tank34 is also preferably temperature controllable, though depending on itsscale.

The function of the apparatus for simultaneous dry desulfurization anddenitration in accordance with a suitable embodiment of the presentinvention is explained next. Referring to FIG. 10, 100% HNO₃ is held atthe pre-designed temperature, its vapor pressure is controlled based ona pressure sensor not shown here, N₂ is bubbled from the gas supplyingsystem 32, and HNO₃ vapor is introduced with carrier gas from the tank34 through the manifold 24. When the exhaust gas 23 of 600-800° C. isintroduced, SO₂ and NO in the exhaust gas 23 are simultaneously oxidizedwith OH radicals as an initiator generated by pyrolysis of HNO₃, SO₃ andNO₂ are formed, and exhausted from the reactor 20. Here, if SO₂concentration in exhaust gas is, for example, 1000 ppm, HNO₃ is alsointroduced at the similar concentration of 1000 ppm. Thus, in thepresent embodiment, simultaneous desulfurization and denitration can berealized only by supplying OH radicals or OH radical initiators into theexhaust gas of high temperature.

FIG. 11 is a reactor in accordance with another embodiment. Referring toFIG. 11, a reactor 30 is comprised of an outer tube 42 set coaxially andclosely with an exhaust gas introducing line 41, and injectors 44, 46,and 48 set at proper length and position, and said injectors 44, 46, and48 are supplied with OH radicals or an OH radical initiators from the OHradical supplier 12.

FIG. 12 is an external view showing an example of an injector. Theinjector 49 shown in FIG. 12(a) is provided with a single blowout hole54 at a tip side, and an injector 55 shown in FIG. 12(b) is providedwith blowout holes 51, 52, 53, and 54 at proper positions, and the sizesof blowout holes are appropriately varied with the conductances ofinjectors taken into consideration. Here, in the example shown in FIG.12, the blowout holes are set at one side of the injector, but they maybe set at both sides. Such the injector is set at the center of thereactor, and supplies OH radicals or OH radical initiators.

In order to desulfurize and denitrate efficiently, it is necessary todetermine the optimum length of the injector, and it has to bepreferably determined depending upon the scale of the apparatus. Also,injectors may be pipes of stainless steel or quartz, but stainless steelis preferred, because of higher decrease ratio of NO and SO₂. In case tointroduce OH radicals or an OH radical initiators with injectors, it iseasy to adjust the positions of blowout holes of injectors in a reactorand the supply quantity so that efficient desulfurization anddenitration are possible depending upon the scale of exhaust gas andexhaust gas treating apparatus.

The OH radical supplier 12 shown in FIG. 11 is to supply HNO₃ vapor orHNO₃ vapor and steam, but it may be an OH radical supplier to supplyHNO₃ droplets. In this case, the injector is changed to spray nozzle,which introduces HNO₃ droplets into the reactor.

FIG. 13 is an outline of a reactor in which HNO₃ droplets are sprayed.Referring to FIG. 13, the reactor 50 has an outer tube 42 set in thedirection vertical to the exhaust gas introducing line 41, a HNO₃recovery apparatus 62 is provided at the exhaust gas introducing inletside of said outer tube 42, and a recycling bath 58 of HNO₃ as an OHradical initiator is provided. Further, shower pipes 56 and 56 areprovided at appropriate positions of the outer tube 42 of the reactor50, and from said shower pipes 56 and 56, an OH radical initiator issupplied by spraying. Here, 59 in FIG. 13 illustrates the mist of OHradical initiators. When said supplied HNO₃ as an OH radical initiatoris cooled and accumulated in a recycling bath 58, the OH radicalinitiator accumulated here is recycled to shower pipes 56 and 56 with apump not shown here. In a reactor 60 shown in FIG. 14, an OH radicalinitiator is supplied with a spray nozzle 57 instead of the shower pipe56 shown in FIG. 13, and 59 in FIG. 14 illustrates the mist of OHradical initiators.

FIG. 15 is of a horizontal type reactor 70, and shower pipes 56 and 56are provided along an outer tube wall. The reactor described above maybe either vertical or horizontal type.

When the exhaust gas of 600-800° C. is introduced into such a reactor,OH radicals supplied from the OH radical supplier or the OH radicalgenerated from pyrolysis of an OH radical initiator acts as an initiatorof the above-mentioned chain reaction to simultaneously oxidize SO₂ andNO in exhaust gas, and SO₃ and NO₂ are exhausted.

Next, a recovery apparatus of sulfuric acid and HNO₃ is explained.

FIG. 16 shows an example of a sulfuric acid recovery apparatus. Thesulfuric acid recovery apparatus is a scrubber 80, provided with a bath82, a packed tub 84, and a shower pipe 86 to spray absorbent, and thecooled exhaust gas containing SO₃ gas is introduced from a gas inlet 87,and exhausted from a gas outlet 88. The absorbent is water in smallquantity, and water and SO₃ gas contact in the packed tube 84 to formsulfuric acid to be stored and recovered in the bath 82. Thus, SO₃ canbe recovered as sulfuric acid by scrubber with water as the absorbent.Since SO₃ can be easily converted to sulfuric acid even under extremelytrace amount of water, it is useful as a byproduct. Also, sulfuric acidmay be recovered as gypsum with calcium carbonate added and reacted withit.

The sprayed HNO₃ is recovered by the above-mentioned HNO₃ recoveryapparatus. Or, after SO₃ is recovered by an electric dust collector, NO₂may be absorbed by a scrubber to be recovered as HNO₃, supplied to theabove-mentioned HNO₃ recovery apparatus and reused.

The present invention is by no way limited to the above-mentionedembodiments, but various modification is possible within the range ofthe invention described in Claims, and needless to say that it is alsoincluded in the present invention. For example, the reactor to blow inOH and OH radicals at multi-steps as explained in the above-mentionedembodiments may of course be properly designed, manufactured, andapplied so as to be attached to various combustion apparatuses dependingupon the flow rate of exhaust gas and SO₂ and NO gas concentrations tobe desulfurized and denitrated.

INDUSTRIAL APPLICABILITY

As is explained above, since said apparatus for simultaneous drydesulfurization and denitration is such that the supplied OH radicalsact as initiators to induce chain reaction, simultaneously oxidize SO₂and NO in exhaust gas, and exhaust them as SO₃ and NO₂, it can treatexhaust gas by dry method without using catalyst or others, as well ashas the effect of high efficiency and low cost.

Also, the apparatus for simultaneous dry desulfurization and denitrationprovided with either or both of a sulfuric acid or HNO₃ recoveryapparatuses has the effect capable of recovery of oxidized SO₃ and NO₂as sulfuric acid and HNO₃, and further an OH radical initiator as HNO₃,in case that HNO₃ is used as the OH radical initiator.

1. An apparatus for simultaneous dry desulfurization and denitrationcharacterized in that, the apparatus for dry exhaust gas treatment totreat exhaust gas of high temperature comprises: a reactor into whichsaid exhaust gas of high temperature is introduced; and a supplier tointroduce nitric acid into said reactor, OH radicals are generated bysaid nitric acid being introduced into said exhaust gas of hightemperature and pyrolyzed, and chain reactions are constituted by saidOH radicals, and both of the sulfur dioxide (SO₂) and the nitrogenmonoxide (NO) in exhaust gas are simultaneously oxidized for exhaust gastreatment.
 2. The apparatus for simultaneous dry desulfurization anddenitration as set forth in claim 1, characterized in that said reactoris provided coaxially with an inner and an outer tubes separated by aspace, and said inner tube is provided with a radical supplying inlet tosupply nitric acid and OH radicals generated by pyrolysis of nitricacid.
 3. The apparatus for simultaneous dry desulfurization anddenitration as set forth in claim 2, characterized in that said innertube is provided with said radical supplying inlets at multi-steps atpre-designed intervals, thereby capable of multi-step blowing-in.
 4. Theapparatus for simultaneous dry desulfurization and denitration as setforth in claim 1, characterized in that said reactor is provided withinjectors to supply nitric acid and OH radicals generated by pyrolysisof nitric acid.
 5. The apparatus for simultaneous dry desulfurizationand denitration as set forth in claim 4, characterized in that saidinjectors are provided as a plurality with different lengths, therebycapable of multi-step blowing-in.
 6. The apparatus for simultaneous drydesulfurization and denitration as set forth in claim 1, characterizedin that said reactor is provided with a shower pipe and/or a spraynozzle to supply either nitric acid and OH radicals generated bypyrolysis of nitric acid.
 7. The apparatus for simultaneous drydesulfurization and denitration as set forth in claim 1, characterizedin that said reactor is either vertical or horizontal type.
 8. Theapparatus for simultaneous dry desulfurization and denitration as setforth in claim 1, characterized in that said supplier to introducenitric acid is provided with nitric acid and a gas supplying system. 9.(canceled)
 10. (canceled)
 11. (canceled)
 12. The apparatus forsimultaneous dry desulfurization and denitration as set forth in claim1, characterized in that said oxides generated from said simultaneousoxidation are sulfur trioxide and nitrogen dioxide.
 13. The apparatusfor simultaneous dry desulfurization and denitration as set forth inclaim 1, characterized to be provided with a sulfuric acid recoveryapparatus to recover sulfur trioxide generated from oxidation treatingof exhaust gas as sulfuric acid and gypsum, or both.
 14. The apparatusfor simultaneous dry desulfurization and denitration as set forth inclaim 1, characterized to be provided with a nitric acid recoveryapparatus to recover nitrogen dioxide generated from oxidation treatingof exhaust gas as nitric acid.
 15. The apparatus for simultaneous drydesulfurization and denitration as set forth in claim 1, characterizedto be provided with a nitric acid recovery apparatus to recover nitricacid.
 16. The apparatus for simultaneous dry desulfurization anddenitration as set forth in claim 15, characterized in that saidrecovered nitric acid is reused by recycling.
 17. A method forsimultaneous dry desulfurization and denitration using an apparatuswhich comprises: a reactor into which an exhaust gas of high temperatureis introduced; and a supplier to introduce nitric acid into saidreactor, characterized in that, OH radicals are generated by said nitricacid being introduced into said exhaust gas of high temperature andpyrolyzed, and chain reactions are constituted by said OH radicals, andboth of the sulfur dioxide (SO₂) and the nitrogen monoxide (NO) inexhaust gas are simultaneously oxidized for exhaust gas treatment. 18.The method for simultaneous dry desulfurization and denitration as setforth in claim 17, characterized in that gas M which does not directlycontribute to reactions is added into said exhaust gas.
 19. The methodfor simultaneous dry desulfurization and denitration as set forth inclaim 18, characterized in that the chain reaction in which said OHradicals are added into the exhaust gas is constituted as,OH+SO₂+M=HOSO₂+M   (R1),OHSO₂+O₂═HO₂+SO₃   (R2), andHO₂+NO═OH+NO₂   (R3).
 20. The method for simultaneous drydesulfurization and denitration as set forth in claim 17, characterizedin that said reaction is conducted under the atmospheric pressure. 21.The method for simultaneous dry desulfurization and denitration as setforth in claim 17, characterized in that said reaction is conducted at atemperature of 650K to 800K.